Element for Anchoring an Anti-Erosion Coating to an Inner Wall of a Chamber of an FCC Unit

ABSTRACT

The invention relates to a metal element ( 12 ) for anchoring an anti-erosion coating that is intended to be fastened alone in an isolated manner to a metal wall or assembled with other identical anchoring elements. The anchoring element ( 12 ) has an edge ( 12   a ) for fastening to said metal wall and an anchoring body firmly attached to the fastening edge ( 12   a ) and having an upper edge ( 12   b ) that is away from the fastening edge and intended to be covered by a composite material of concrete type. A section of this upper edge ( 12   b ), which is not intended to be juxtaposed and assembled with an upper edge of an identical anchoring element, is provided with a delimiting tab ( 16 ) in order to delimit a height of composite material that must cover the upper edge ( 12   b ) of said anchoring element, said delimiting tab ( 16 ) having a delimiting edge ( 18 ) that is a predetermined distance away from a plane defined by the upper edge ( 12   b ) of the anchoring element.

The invention relates to an element for anchoring an anti-erosioncoating to an inner or outer wall of a chamber of a fluid catalyticcracking (FCC) unit.

The invention relates in particular to an element for anchoring ananti-erosion coating that is intended to protect a wall of a cyclone,reactor plenum, stripper, riser, downer, standpipes, withdrawal wells ordisengager that is part of a fluid catalytic cracking unit.

The invention also relates to an anchoring structure formed from theassembly of anchoring elements according to the invention, a coatingusing anchoring elements or an anchoring structure according to theinvention and a process for producing an anti-erosion coating usinganchoring elements according to the invention.

The metal walls of the various chambers of an FCC unit, such as forexample a disengager and a regenerator, and the metal walls of theinternal equipment located in the regenerator or the disengager, inparticular the cyclones, may undergo erosion due to the circulation ofthe catalyst particles in the unit, and, at the regenerator, a bulkcorrosion by the gases produced during the combustion that makes itpossible to regenerate the catalyst. It is therefore necessary toprotect these metal walls in order to lengthen their service life.

The metal walls of the chambers of a catalytic cracking unit and of theequipment inside these chambers are thus covered with a coating intendedto protect them mainly from erosion. Such coatings generally consist ofa composite material, generally a concrete, held by an anchoringstructure, which is usually metallic. These anchoring structures arewelded to the metal walls and thus provide the attachment of thecomposite material. They may be in various forms. Thus, they may be aplurality of hexagonal cells firmly attached to one another by one sideso as to form a honeycomb structure (Hexmesh®). Use is also made ofstrips of S-shape, K-shape or any other geometric shape, extendingparallel to the wall, anchored in the wall by a support footperpendicular to the wall. Such S-shaped or K-shaped strips are alsoreferred to as “S bars” or “K bars” and are rather used in an isolatedmanner, for example on surfaces of complex geometry that cannot receivea honeycomb anchoring structure. Hexagonal-shaped anchoring elements arealso used in an isolated manner for anchoring to surfaces of complexgeometry. Like S bars, these hexagonal-shaped anchoring elements are,most often, used in isolation, without contact with adjacent anchoringelements. Honeycomb-type structures also exist having square cellsformed of strips connected in pairs by rods forming axes of rotation(Flexmesh®). This type of structure has the advantage of being able toclosely fit a curved wall without prior shaping.

After fastening these anchoring elements to the metal wall to beprotected, a composite material is applied to the metal wall equippedwith anchoring elements so as to cover the latter. However, thiscomposite material is generally applied and smoothed using a board(float or trowel) pressing against the anchoring elements, so that inpractice the concrete is flush with the top of the anchoring elements.It may happen that certain anchoring elements are not completely coveredwith concrete and that interstices remain that enable the diffusion ofgases between the concrete and the anchoring, or between two assembledanchorings. The penetration of catalyst particles into these intersticesis also possible at these locations.

Moreover, the difference in expansion coefficient between the metalanchoring and the concrete causes, when they are exposed to hightemperature under the operating conditions of the FCC unit, theappearance of interstices between the side walls of the concretebiscuits and the anchoring, here again enabling the diffusion of thegaseous species resulting from the process and of catalyst.

When this coating is in contact with the gases resulting from thecracking of the feedstock, for example in the disengager or on thecyclones located in the disengager, these gases may lead to theformation of coke inside these interstices. This formation of coke maylead to a significant detachment of the coating during successivecooling/heating cycles of the chamber.

When the coating is in contact with a gas containing, inter alia,oxygen, carbon oxides, sulfur and nitrogen, such as for example thegases present in a regenerator or in the internal equipment of aregenerator, in particular the cyclones, plenum, standpipe, this gaspenetrates through the interstices of the coating and causessulphidation, carburization and oxidation phenomena, in particular atthe welds that fasten the metal anchoring structure to the metal walls,which may cause a disconnection of the anchoring structure.

Irrespective of the degradation phenomena observed, corrosion,especially by sulphidation, carburization, oxidation or formation ofcoke, the applicant has observed that these phenomena essentially occurat the metal anchoring structure and/or its bonding via welding to themetal walls, and in particular at the juxtaposed parts of the anchoringstructure in the case of honeycomb-shaped anchoring structures.

There is therefore a need for an anti-erosion coating anchoring elementthat is more resistant to the degradation phenomena, in particular tocorrosion, especially by sulphidation, carburization, oxidation orformation of coke.

In order to solve this problem, the applicant has proposed, inapplication WO 2014/0092625 A1, a particular process for producing acoating for a honeycomb anchoring structure, which especially compriseda particular step of fastening by welding of the anchoring structure. Itwas also proposed to produce honeycomb structures having differentheights at their assembled walls in order to promote the filling of theinterstices between these assembled walls with the composite material.The process described does not however relate to the anchoring elementsused in an isolated manner.

The invention aims to overcome the aforementioned drawbacks by proposinga metal element for anchoring an anti-erosion coating to an inner orouter metal wall of a chamber of a fluid catalytic cracking unit, saidelement being intended to be fastened alone in an isolated manner tosaid metal wall, such as for example the anchoring elements of S-bar orK-bar type or of hexagonal shape mentioned above, or being intended tobe fastened to said metal wall assembled with other identical anchoringelements, such as the honeycomb anchoring structures (Hexmesh®,Flexmesh®).

The anchoring element according to the invention has a fastening edgeintended to be fastened to the metal wall to be protected and ananchoring body firmly attached to the fastening edge, said anchoringbody having an upper edge that is away from the fastening edge andintended to be covered by a composite material of concrete type, thisupper edge defining a plane.

According to the invention, at least one section of the upper edge,which is not intended to be juxtaposed and assembled with an upper edgeof another identical anchoring element, is provided with a delimitingtab in order to delimit a height of composite material that must coverthe upper edge of said anchoring element, said delimiting tab having adelimiting edge that is a predetermined distance away from the planedefined by the upper edge of the anchoring element.

Thus, this delimiting tab will serve as a marker during the applicationof the composite material, the worker being able to smooth the compositematerial to the height of the delimiting edge of this delimiting tabwith the smoothing tool (float or trowel). In this way, the rest of theanchoring element, in particular the rest of the upper edge, locatedfurther back with respect to the delimiting tab, is covered with a layerof composite material at least equal to the predetermined distance,making it possible to limit the formation of an interstice that lets thecorrosive gases through.

Moreover, the applicant has observed that the creation of a delimitingtab on a part of the anchoring element not assembled with anotheranchoring element makes it possible to reduce the formation ofinterstices between the assembled parts after application of thecomposite material.

The predetermined distance may be selected so that, once dry, thecomposite material of concrete type is still flush with the delimitingtab or tabs. By way of example, this distance may be at least 2 mm, forexample less than or equal to 10 mm, preferably less than or equal to 6mm, or even less than or equal to 3 mm.

Advantageously and non-limitingly, the section may extend over a part ofthe length of the upper edge. For example, the delimiting tab may extendat most over ½ or at most over ¼ of the length of the upper edge, inparticular of the length of the section of the upper edge provided withthe delimiting tab, this being in order to limit the potential zones forintroducing gas. Indeed, it is sufficient for the delimiting tab toproject from the upper edge in order to be able to be spotted by theworker applying the composite material. By way of example, the length ofthe delimiting tab, and in particular of its delimiting edge, is from 10to 22 mm.

The delimiting tab may be positioned in the middle of said upper edge,which may simplify the production of the anchoring element.

Advantageously and non-limitingly, the anchoring body may be formed byfolding or bending a flat strip along an axis perpendicular to alongitudinal direction of the strip, in the plane of the strip, and saiddelimiting tab extends in the continuation of said flat stripperpendicular to said longitudinal direction. In other words, thedelimiting tab then corresponds to a zone of the flat strip of greaterwidth. The delimiting tab may thus be obtained simply, in particularwhen it is produced from one part with the anchoring body.

Advantageously and non-limitingly, the anchoring element is made ofstainless steel (a stainless steel contains at most 1.2% by weight ofcarbon and at least 10.5% by weight of chromium according to the EN10008standard). In particular, the stainless steel will be able to beselected so as to withstand the environment of the chamber in which theanchoring structure must be used.

The anchoring element may thus be made of austenitic stainless steelselected from the following steels:

-   -   a stainless steel containing from 0.04% to 0.10% by weight of        carbon, from 18% to 20% by weight of chromium and from 8% to        10.5% by weight of nickel, and with a manganese content of at        most 2% by weight, for example a steel of AISI 304H grade,    -   a stainless steel containing from 0.04% to 0.10% by weight of        carbon, from 17% to 19% by weight of chromium and from 9% to 12%        by weight of nickel, and with a niobium content of from 8 times        the carbon content to 1% by weight, for example a steel of AISI        347 grade,    -   a stainless steel containing at most 0.015% by weight of carbon,        from 15% to 17% by weight of chromium and from 33% to 37% by        weight of nickel, for example a steel of AISI 330 grade,    -   a stainless steel containing at most 0.10% by weight of carbon,        from 24% to 26% by weight of chromium and from 19% to 22% of        nickel, for example a steel of AISI 310 grade,    -   a stainless steel containing at most 0.08% by weight of carbon,        from 17% to 19% by weight of chromium, from 9% to 12% by weight        of nickel, a titanium content of from 5 times the carbon content        to 0.70% by weight, a manganese content of at most 2% by weight,        a silicon content of at most 1% by weight, for example a steel        of AISI 321 grade,    -   a stainless steel containing at most 0.15% by weight of carbon,        from 11.5% to 13.5% by weight of chromium, a manganese content        of at most 1% by weight, a silicon content of at most 1% by        weight, for example a steel of AISI 410 grade.

Such austenitic stainless steels may make it possible to reduce thedegradations due to a loss of the stainless nature of the steel by adrop in the chromium content below 10.5% by weight within the steel.

The anchoring element according to the invention may be intended to befastened to the metal wall without contact with another anchoringelement.

According to one embodiment, the upper edge of the anchoring body maythen have an S shape and the section of the upper edge provided with adelimiting tab may be a curved section. The delimiting tab may then bepositioned substantially in the middle of the upper edge of theanchoring body.

In this embodiment, the fastening edge may be part of a foot firmlyattached to the anchoring body, so that the fastening edge is away fromthe anchoring body. Such a fastening foot may also extend in thecontinuation of the anchoring body, in the middle thereof.

Such an anchoring element may be produced by bending a flat strip alongan axis perpendicular to a longitudinal direction of the strip.Optionally, the strip may be precut in order to form the delimiting taband the fastening foot, the rest of the strip having a constant width.

According to another embodiment, the upper edge of the anchoring bodyhas a K shape and the section of the upper edge provided with adelimiting tab is a straight section.

According to another embodiment, the upper edge of the anchoring bodymay have a hexagonal shape and said at least one section of the upperedge provided with a delimiting tab may be part of a straight side ofthe hexagonal shape.

Preferably, the section does not then extend over the whole of thelength of one straight side.

Advantageously, at least two opposite sides of said upper edge ofhexagonal shape may be provided with a delimiting tab, which mayfacilitate an arrangement of a coating layer of uniform thickness on topof the anchoring element owing to the two markers formed by the oppositedelimiting tabs.

Such an anchoring element may be produced by folding a flat strip alongan axis perpendicular to a longitudinal direction of the strip, thenassembling the ends of the strip in order to form a hexagon. Optionally,the strip may be precut in order to form the delimiting tab. Thefastening edge then also has a hexagonal shape and defines a planedifferent from the plane of the upper edge.

The anchoring element according to the invention may also be intended tobe fastened to the metal wall, assembled with other identical anchoringelements in order to form a honeycomb-type anchoring structure. The bodyof said anchoring element may then be formed from a strip divided alongits length into a plurality of portions, first strip portions extendingin a first plane parallel to the longitudinal direction (L) of thestrip, second strip portions extending in a second plane parallel to thefirst plane and different from the first plane, third strip portionseach connecting a first strip portion to a second strip portion, thefirst and second strip portions being alternated over the entire lengthof the strip.

According to the invention, said at least one section of the upper edgeprovided with a delimiting tab of each anchoring element may then bepart of an upper edge of a third portion of the strip of this anchoringelement.

Preferably, the section does not then extend over the whole of thelength of the upper edge of a third portion of the strip.

Advantageously, each third portion of a strip of an anchoring elementmay be provided with a delimiting tab, which may promote the obtainingof a coating of composite material of uniform thickness over the entirearea of the anchoring structure. However, provision may be made for onethird portion out of two or three only to be provided with a delimitingtab.

Such anchoring elements may be assembled in various ways.

According to a first embodiment, the first portions of a strip of ananchoring element are intended to be juxtaposed and assembled with thesecond portions of an adjacent strip so as to form hexagonal cells.Thus, the delimiting tab is not on a portion assembled with anotheranchoring element. In other words, the assembled portions of twoanchoring elements are then of the same height (in a lower plane).

The invention thus also relates to a honeycomb structure for anchoringan anti-erosion coating to an inner or outer metal wall of a chamber ofa fluid catalytic cracking unit formed from an assembly of the anchoringelements described above, in particular of identical anchoring elements,in which the first portions of a strip of an anchoring element arejuxtaposed and assembled with the second portions of a strip of anadjacent anchoring element so as to form hexagonal cells.

According to another embodiment, each first portion joined to two thirdportions of a same anchoring element has a U shape which is intended tobe partly nested in the U shape of each first portion joined to twothird portions of an adjacent anchoring element so that the thirdportions of two adjacent anchoring elements are partly juxtaposed. Thesejuxtaposed parts of the third portions of assembled anchoring elementsare then passed through by a rod extending in the longitudinal directionof the strips of the adjacent anchoring elements, the concavities of theU shapes being pointed in a same direction. Such an arrangement enablesa rotation of two adjacent anchoring elements about the assembly rods.

The delimiting tabs could, as a variant, be provided on the upper edgeof the first and second portions of an anchoring element of this type.However, for an easier arrangement of the composite material, it ispreferable that the section of the upper edge provided with a delimitingtab of each anchoring element is part of an upper edge of a thirdportion of the strip of said anchoring element.

The invention also relates to a honeycomb structure for anchoring ananti-erosion coating to an inner or outer metal wall of a chamber of afluid catalytic cracking unit formed from an assembly of the anchoringelements described above, in particular of identical anchoring elements,in which each first portion joined to two third portions of a sameanchoring element has a U shape partly nested in the U shape of eachfirst portion joined to two third portions of an adjacent anchoringelement so that the third portions of two adjacent anchoring elementsare partly juxtaposed, the concavities of the U shapes being pointed ina same direction so as to form four-sided cells, these juxtaposed partsof the third portions of adjacent anchoring elements being passedthrough by a rod extending in the longitudinal direction (L) of thestrips of the adjacent anchoring elements.

An anchoring structure according to the invention may additionallycomprise one or more of the anchoring elements described above. It mayin particular comprise a plurality of anchoring elements of differentshapes, some of which may be identical to one another and optionallyassembled, each anchoring element having one delimiting tab at least,the delimiting edge of which is located at a same distance from itsupper edge and from its lower edge.

The invention additionally relates to an anti-erosion coating comprisingat least one anchoring element according to the invention embedded in acomposite material, for example a concrete, the composite materialextending up to the delimiting edge of said delimiting tab, above theupper edge of said at least one anchoring element, so that the compositematerial covers or is flush with the delimiting edge of said delimitingtab. Interstices are thus less capable of forming with such a coating,in particular at the zones of contact of the anchoring element and ofthe composite material or between zones of contact of two assembledanchoring elements. The risk of formation of interstices, andconsequently a degradation of the coating, could be reduced even morewhen the length of the delimiting tabs is short, for example less thanor equal to 22 mm, preferably less than or equal to 15 mm.

The composite material, within the meaning of the present invention, ispreferably a material resulting from an assembly of at least twoimmiscible materials having a high adhesion capacity.

Preferably, the composite material is a composite construction materialsuch as a concrete, in particular a concrete suitable for use in a fluidcatalytic cracking unit.

The anti-erosion coating may comprise one or more isolated anchoringelements according to the invention, intended to be fastened alone in anisolated manner to said metal wall, in other words without contact withan adjacent anchoring element.

As a variant or in combination, the anti-erosion coating may compriseseveral anchoring elements according to the invention assembled withother identical anchoring elements in order to form an anchoringstructure, for example a honeycomb anchoring structure.

Advantageously, the anti-erosion coating may comprise a plurality ofanchoring elements of different shapes, optionally in combination with aplurality of assembled identical anchoring elements, each anchoringelement having at least one delimiting tab, the delimiting edge of whichis located at a same distance from its upper edge and from its loweredge. A coating of uniform thickness over the entire surface of the wallto be protected may thus be obtained.

The invention also relates to a chamber of a fluid catalytic crackingunit comprising at least one inner or outer metal wall covered with atleast one coating according to the invention, the fastening edge of eachanchoring element being fastened by welding to the inner or outer wallof the chamber.

Advantageously and non-limitingly, the metal wall to which the coatingis applied is an inner or outer wall of a cyclone, of a regenerator, ofa disengager or of any other internal equipment of a fluid catalyticcracking unit, such as a riser, stripper, standpipe, flue gas line,transfer line between reactor and fractionator, orifice chamber, slidevalve or withdrawal wells.

The invention finally relates to a process for producing an anti-erosioncoating on an inner or outer metal wall of a chamber of a fluidcatalytic cracking unit, comprising:

-   -   (i) the fastening of a plurality of anchoring elements according        to the invention, optionally certain anchoring elements being        preassembled with one another, to said metal wall, this        fastening being carried out by welding to the metal wall of the        fastening edge of each anchoring element,    -   (ii) the application of a layer of a composite material to the        metal wall, the thickness of this layer being selected so that        the composite material covers or is flush with the delimiting        edge of the delimiting tabs of each anchoring element.

The composite material is thus applied so as the remaining part of theupper edge of each anchoring element is covered by a layer of compositematerial, the thickness of which is at least equal to the predetermineddistance previously defined.

The invention is now described with reference to the appended,non-limiting drawings, in which:

FIG. 1 is a representation, in perspective, of anchoring elementsaccording to one embodiment of the invention that form ahoneycomb-shaped anchoring structure;

FIG. 2 is a cross-sectional view along the line A-A of the anchoringstructure represented in FIG. 1, the anchoring structure being fastenedto a metal wall and embedded in a composite material;

FIG. 3 is a cross-sectional view along the line B-B of the anchoringstructure represented in FIG. 1, the anchoring structure being fastenedto a metal wall and embedded in a composite material;

FIG. 4 is a representation, in perspective, of an anchoring elementaccording to a second embodiment of the invention;

FIG. 5 is a representation, in perspective, of an anchoring elementaccording to a third embodiment of the invention;

FIG. 6 is a representation, in perspective, of anchoring elementsaccording to a fourth embodiment of the invention that form ahoneycomb-type anchoring structure, the cells of which have four sides.

FIG. 1 partially represents a honeycomb metal anchoring structure 10formed of a plurality of strips 12 assembled in pairs so as to form aplurality of hexagonal cells 14 connected by their sides to one another.Each strip 12 forms an anchoring element according to a first embodimentof the invention.

The term “strip” is understood to mean a strip of metal material havinga width smaller than a length and a thickness smaller than the width.Preferably, the strip has a constant width over its entire length, withthe exception of the delimiting tabs, as will be described below.

By way of example, the internal dimensions of the cells may vary from 4to 6 cm for a thickness of around 1.5 to 3.0 cm, for example of 2 cm.

Each strip 12, made from one part, is divided along its length into aplurality of portions 121, 122, 123:

-   -   first strip portions 121 that extend in a first plane parallel        to the longitudinal direction L of the strip,    -   second strip portions 122 that extend in a second plane parallel        to the first plane and different therefrom,    -   third strip portions 123 that each connect a first strip portion        121 to a second strip portion 122.

Such an anchoring element 12 may be produced by folding a flat stripalong a direction perpendicular to its longitudinal direction (L), inthe plane of the strip.

The first strip portions 121 and second strip portions 122 arealternated over the entire length of a strip 12 and the first portions121 of one strip are juxtaposed and assembled with the second portions122 of an adjacent strip 12, for example by welding and/or by fasteningmeans. The first strip portions 121 and second strip portions 122 thusform portions for assembly to an adjacent strip 12.

The anchoring structure 10 represented is here formed of a plurality ofidentical strips 12. Each strip 12 has a lower longitudinal edge 12 acontained in a single plane and an upper longitudinal edge 12 b parallelto the lower longitudinal edge 12 a. This longitudinal edge 12 b definesa single plane with the except of the delimiting tabs.

The lower longitudinal edge 12 a forms a fastening edge of the anchoringelement 12, the strip 12 by itself forming an anchoring body within themeaning of the invention.

According to the invention, a section of the upper edge 12 b, which isnot intended to be juxtaposed and assembled with an upper edge of anidentical adjacent anchoring element, is provided with a delimiting tab16 in order to delimit a height of composite material that must coverthe upper edge of the anchoring element. For this purpose, thedelimiting tab 16 has a delimiting edge 18 that is a predetermineddistance away from the plane defined by the upper edge 12 b of theanchoring element 12. In other words, in the present example, as seen inFIG. 1, the delimiting edge 18 of the delimiting tab 16 extends parallelto the lower edges 12 a and upper edges 12 b.

FIGS. 2 and 3 are cross-sectional views along the lines A-A and B-B fromFIG. 1, to the same scale. In these figures, a metal wall 20 isdistinguished, to which the anchoring structure 10 is fastened. Thisfastening is carried out by welding the fastening edge 12 a to the wall20. FIG. 2 represents assembled portions 121 and 122 of the anchoringstructure. A layer 21 of composite material covers the upper edges 12 bof these assembly portions 121, 122. This layer 21 extends over a heightH (measured from the metal wall 20, perpendicular thereto) so that thesurface of the layer 21 of composite material is flush with thedelimiting edge 18 of the delimiting tab 16 (FIG. 3). Thus, for a stripof height h (in other words of width h), a thickness d of compositematerial 21 covers the upper edges 12 b of the anchoring element, thetotal height H of the layer 21 being equal to the sum of the height hand of the thickness d. This thickness d thus corresponds to thepredetermined distance separating the delimiting edge 18 from the planedefined by the upper edge 12 b of the anchoring element 12.

By thus using the delimiting edges 18 of the tabs 16 to produce acoating of predetermined thickness, one is certain to completely coverthe anchoring element 12, in particular its assembly portions 121, 122and to thus avoid the formation of interstices, and a layer of compositematerial of uniform thickness is produced.

In the example, each third portion 123 is provided with a delimiting tab16, which extends over a part of the length of the upper edge of thisthird portion 123.

As represented in FIG. 1, an anchoring element 12 may additionally havea flap of material 22 cut from at least one portion other than anassembly portion (i.e. here a portion 123) and folded in order to jutout from this portion. Such a configuration may make it possible toimprove the anchoring of the composite material to the anchoringelement, the flap then being embedded in the composite material, thehold of which is also strengthened due to the fact that it passesthrough the orifice freed up by the folded-out flap.

The flaps 22 of material resulting from portions that are part of a samecell may be folded out towards one another. This arrangement makes itpossible to obtain two flaps folded out towards the centre of each cellwhen the strips are assembled with one another.

These flaps 22 may also be folded out so as to extend substantiallyparallel to the planes of the strip assembly portions.

The anchoring structure 10 represented in FIG. 1 may be shaped beforethe fastening thereof to a metal wall, for example by roll bending inorder to closely match the shape of this metal wall.

When the metal wall to be protected has a more complex shape, it maythen be difficult, or even impossible, to fasten an anchoring structureof the type of that described with reference to FIG. 1. It is thenpossible to use isolated anchoring elements of the type of thosedescribed with reference to FIGS. 4 and 5, or articulated anchoringelements, of the type of those described with reference to FIG. 6.

FIG. 4 represents an anchoring element 12′ according to anotherembodiment of the invention.

The anchoring element 12′ has an anchoring body 13, the upper edge 13 bof which has an S shape, defines in the plane of the upper edge 13 b.Here, this anchoring body 13 is in the form of a flat strip bent along adirection perpendicular to its longitudinal direction, in the plane ofthe strip. The lower edge 13 a of this anchoring body 13 is firmlyattached to a support foot 13 c that extends perpendicular to thelongitudinal direction of the strip. This support foot 13 c has afastening edge 13 d, via which the anchoring element 12′ may be weldedto the metal wall to be protected.

According to the invention, an optionally curved section of the upperedge 13 b comprises a delimiting tab 16′, the delimiting edge 18′ ofwhich is a predetermined distance d′ away from the plane defined by theupper edge 13 b. The length of the delimiting tab 16′, i.e. here thelength of the optionally curved section, is preferably equal to aquarter or less of the total length of the upper edge 13 b.

Such an anchoring element 12′ is intended to be fastened to the metalwall without contact with another anchoring element.

FIG. 5 represents an anchoring element 12″ according to yet anotherembodiment of the invention.

This anchoring element 12″ has a hexagonal shape. It is obtained byfolding a flat strip along a direction perpendicular to the longitudinaldirection of the strip, in the plane of the strip, the ends of the stripbeing joined in order to close up the hexagonal shape. The structureobtained thus forms a cell that may be filled and covered with compositematerial. The anchoring element 12″ has a lower edge 12″a forming afastening edge, via which it may be welded to a metal wall to beprotected. The folded strip by itself forms an anchoring body. Theanchoring element 12″ has an upper edge 12″b of hexagonal shape thatdefines a plane, here parallel to the plane of the lower edge 12″a.

According to the invention, a section of the upper edge 12″b comprises adelimiting tab 16″, the delimiting edge 18″ of which is a predetermineddistance d″ away from the plane defined by the upper edge 12″b. Here,the anchoring element 12″ has two delimiting tabs 16″ positioned onopposite edges of the hexagonal shape. These tabs 16″ are thus parallel,which may facilitate the application of the composite material.

The length of the delimiting tab 16″, i.e. here the length of thestraight section, is preferably equal to half or less of the totallength of the upper edge 12″b.

As for the embodiment described above, the anchoring element 12″ isintended to be fastened to the metal wall without contact with anotheranchoring element. The presence of a delimiting tab 16′ or 16″ in thesetwo embodiments then makes it possible to ensure that the rest of theupper edge 13 b or 12″b of the anchoring body is completely covered withcomposite material, thus limiting the risks of infiltrations ofcorrosive gas between the anchoring element and the composite material,while maintaining a constant height of composite material owing to themarker of the delimiting tab.

FIG. 6 represents a metal anchoring structure 10′ of honeycomb typeformed from a plurality of anchoring elements 12′″ according to yetanother embodiment of the invention.

This embodiment is similar to that described with reference to FIG. 1,each anchoring element 12′″ being formed from a strip, these stripsbeing assembled in pairs so as to form a plurality of four-sided cells.The term “strip” has the same meaning as that already given. Thesestrips may be produced as already described for the first embodiment.

Each strip 12′″, made from one part, is divided along its length into aplurality of portions 121′″, 122′″, 123′″:

-   -   first strip portions 121′″ that extend in a first plane parallel        to the longitudinal direction L of the strip,    -   second strip portions 122′″ that extend in a second plane        parallel to the first plane and different therefrom,    -   third strip portions 123′″ that each connect a first strip        portion 121′″ to a second strip portion 122′″.

The first strip portions 121′″ and second strip portions 122′″ arealternated over the entire length of a strip 12′″. Here, each firstportion 121′″ joined to two third portions 123′″ of a same anchoringelement has a U shape which is partly nested in the U shape of eachfirst portion 121′″ joined to two third portions 123′″ of an adjacentanchoring element so that the third portions 123′″ of two adjacentanchoring elements are partly juxtaposed, forming four-sided cells (FIG.6). The concavities of the U shapes thus defined are all pointed in asame direction. These juxtaposed parts 23 of the third portions 123′″ ofadjacent anchoring elements are additionally passed through by a rod 24extending in the longitudinal direction L of the strips of the adjacentanchoring elements.

An articulated anchoring structure 10′ is thus obtained, it beingpossible for each anchoring element 12′″ to pivot with respect to anadjacent anchoring element 12′″ by rotation about a rod 24.

The anchoring structure 10′ represented is here formed of a plurality ofidentical strips 12′″. Each strip 12′″ has a lower longitudinal edge12′″a contained in a single plane and an upper longitudinal edge 12′″bparallel to the lower longitudinal edge 12′″a.

The lower longitudinal edge 12′″ a forms a fastening edge of theanchoring element 12′″, the strip 12′″ by itself forming an anchoringbody within the meaning of the invention.

According to the invention, a section of the upper edge 12′″b, which isnot intended to be juxtaposed and assembled with an upper edge of anidentical adjacent anchoring element, is provided with a delimiting tab16′″ in order to delimit a height of composite material that must coverthe upper edge of the anchoring element. For this purpose, thedelimiting tab 16′″ has a delimiting edge 18′″ that is a predetermineddistance d′″ away from the plane defined by the upper edge 12′″b of theanchoring element 12′″. In other words, the delimiting edge 18′″ of thedelimiting tab 16′″ extends parallel to the lower edges 12′″a and upperedges 12′″b.

In the example, each third portion 123′″ is provided with a delimitingtab 16′″, which extends over a part of the length of the upper edge ofthis third portion 123′″ not juxtaposed with a third portion 123′″ of anadjacent anchoring element 12′″. Such an arrangement facilitates thepositioning of the composite material.

Thus, by using anchoring elements of different shape but that all have adelimiting tab positioned at a same distance from their fastening edge,it is possible to produce a coating with a constant thickness. In allthe embodiments represented, the delimiting tab 16, 16′, 16″, 16′″extends in the continuation of a strip forming the anchoring body. Thefastening edge may be part of this strip, for example when it is a loweredge, or may be firmly attached to the strip.

Advantageously, irrespective of the embodiment of an anchoring element,the delimiting tab or tabs are preferably made from one piece with theanchoring body, for example by cutting a strip of constant width, andthen shaping this strip, by folding or bending. In the same way, thefastening edge is advantageously integrated into the anchoring body.

It will also be noted that one or more flaps, similar to the flaps 22described with reference to the embodiment represented in FIG. 1, may beprovided on the anchoring bodies of the anchoring elements describedwith reference to FIGS. 4 to 6 in order to improve the anchoring of thecomposite material by the anchoring element.

1.-14. (canceled)
 15. A process for producing an anti-erosion coating onan inner or outer metal wall of a chamber of a fluid catalytic crackingunit, comprising: fastening a plurality of metal anchoring elements onthe metal wall, each anchoring element being fastened alone in anisolated manner to the metal wall or being fastened to the metal wallassembled with other identical anchoring elements, the fastening beingcarried out by welding to the metal wall a fastening edge of eachanchoring element, each anchoring element having: a fastening edgefastened to the metal wall, and an anchoring body firmly attached to thefastening edge, the anchoring body having an upper edge that is awayfrom the fastening edge and defining a plane, wherein at least onesection of the upper edge, which is not juxtaposed and assembled with anupper edge of another identical anchoring element, is provided with adelimiting tab in order to delimit a height of composite material thatmust cover the upper edge of the anchoring element, the delimiting tabhaving a delimiting edge that is a predetermined distance away from theplane defined by the upper edge of the anchoring element, wherein theanchoring element is intended to be fastened to the metal wall withoutcontact with another anchoring element, the anchoring element having afastening edge intended to be fastened to the metal wall, and ananchoring body firmly attached to the fastening edge, the anchoring bodyhaving an upper edge that is away from the fastening edge and intendedto be covered by a composite material of concrete type, the upper edgedefining a plane, characterized in that: at least one section of theupper edge is provided with a delimiting tab in order to delimit aheight of composite material that must cover the upper edge of theanchoring element, the delimiting tab having a delimiting edge that is apredetermined distance (d′) away from the plane defined by the upperedge of the anchoring element, the upper edge of the anchoring body hasan S shape, and the section of the upper edge provided with a delimitingtab is a curved section. (ii) applying a layer of a composite materialto the metal wall, the thickness of this layer being selected so thatthe composite material covers or is flush with the delimiting edge ofthe delimiting tabs of each anchoring element and so that the remainingpart of the upper edge of each anchoring element is covered by a layerof composite material, the thickness of which is at least equal to thepredetermined distance.
 16. The process of claim 15 wherein thedelimiting tab is positioned substantially in the middle of the upperedge of the anchoring body.
 17. The process of claim 15 furthercomprising forming the anchoring body by folding or bending a flat stripalong an axis perpendicular to a longitudinal direction (L) of thestrip, in the plane of the strip, and in that the delimiting tab extendsin the continuation of the flat strip perpendicular to the longitudinaldirection.
 18. The process of claim 15 wherein the anti-erosion coatingcomprises at least one of the anchoring elements embedded in thecomposite material, the composite material extending up to thedelimiting edge of the delimiting tab, above the upper edge of the atleast one anchoring element, so that the composite material covers or isflush with the delimiting edge of the delimiting tab and so that theremaining part of each anchoring element is covered by a layer of thecomposite material, the thickness of which is at least equal to thepredetermined distance.